Conventional semiconductor devices generally include a semiconductor substrate, usually a silicon substrate, and a plurality of sequentially formed dielectric interlayers such as silicon dioxide and conductive paths or interconnects made of conductive materials. Copper and copper alloys have recently received considerable attention as interconnect materials because of their superior electromigration and low resistivity characteristics. The interconnects are usually formed by filling copper in features or cavities etched into the dielectric interlayers by a metallization process. The preferred method of copper metallization process is electroplating. In an integrated circuit, multiple levels of interconnect networks laterally extend with respect to the substrate surface. Interconnects formed in sequential interlayers can be electrically connected using vias or contacts.
In a typical process, first an insulating interlayer is formed on the semiconductor substrate. Patterning and etching processes are performed to form features such as trenches and vias in the insulating layer. Then, copper is electroplated to fill all the features. However, the plating process results in a thick copper layer on the substrate some of which need to be removed before the subsequent step. Conventionally, after the copper plating, CMP process is employed to globally planarize or reduce the thickness of the copper layer down to the level of the surface of the insulation layer. However, CMP process is a costly and time consuming process that reduces production efficiency.
The adverse effects of conventional material removal technologies may be minimized or overcome by employing an Electrochemical Mechanical Processing (ECMPR) approach that has the ability to provide thin layers of planar conductive material on the workpiece surface, or even provide a workpiece surface with no or little excess conductive material. The term of Electrochemical Mechanical Processing (ECMPR) is used to include both Electrochemical Mechanical Deposition (ECMD) processes as well as Electrochemical Mechanical Etching (ECME), which is also called Electrochemical Mechanical Polishing. It should be noted that in general both ECMD and ECME processes are referred to as electrochemical mechanical processing (ECMPR) since both involve electrochemical processes and mechanical action.
FIG. 1 shows an exemplary conventional ECMPR system 2, which system 2 includes a workpiece-surface-influencing device (WSID) 3 such as a mask, pad or a sweeper, a carrier head 4 holding a workpiece 5 and an electrode 6. The workpiece-surface-influencing-device (WSID) is used during at least a portion of the electrotreatment process when there is physical contact or close proximity and relative motion between the workpiece surface and the WSID. Surface of the WSID 3 sweeps the surface of the workpiece 5 while an electrical potential is established between the electrode 6 and the surface of the workpiece. Channels 7 of the WSID 3 allow a process solution 8 such as an electrolyte to flow to the surface of the workpiece 5. If the ECMD process is carried out, the surface of the workpiece 5 is wetted by a deposition electrolyte which is also in fluid contact with the electrode (anode) and a potential is applied between the surface of the workpiece and the electrode rendering the workpiece surface cathodic. If the ECME process is carried out, the surface of the workpiece 5 is wetted by the deposition electrolyte or a special etching electrolyte, which is also in fluid contact with an electrode (cathode) and a potential is applied between the surface of the workpiece and the electrode rendering the workpiece surface anodic. Thus etching takes place on the workpiece surface. Very thin planar deposits can be obtained by first depositing a planar layer using an ECMD technique and then using an ECME technique on the planar film in the same electrolyte by reversing the applied voltage. Alternately, the ECME step can be carried out in a separate machine and a different etching electrolyte. The thickness of the deposit may be reduced in a planar manner.
Descriptions of various planar deposition and planar etching methods i.e. ECMPR approaches and apparatus can be found in the following patents and pending applications, all commonly owned by the assignee of the present invention. U.S. Pat. No. 6,126,992 entitled “Method and Apparatus for Electrochemical Mechanical Deposition.” U.S. application Ser. No. 09/740,701 entitled “Plating Method and Apparatus that Creates a Differential Between Additive Disposed on a Top Surface and a Cavity Surface of a Workpiece Using an External Influence,” filed on Dec. 18, 2001, and application Ser. No. 09/169,913 filed on Sep. 20, 2001, entitled “Plating Method and Apparatus for Controlling Deposition on Predetermined Portions of a Workpiece”. These methods can deposit metals in and over cavity sections on a workpiece in a planar manner. They also have the capability of yielding novel structures with excess amount of metals selectively over the features irrespective of their size, if desired.
The surface of the WSID preferably contains hard-abrasive material for efficient sweeping. U.S. application Ser. No. 09/960,236 filed on Sep. 20, 2001, entitled “Mask Plate Design,”,U.S. Provisional Application Ser. No. 60/326,087 filed on Sep. 28, 2001, entitled “Low Force Electrochemical Mechanical Processing Method and Apparatus,” and U.S. application Ser. No. 10/155,828 filed May 23, 2002, all of which are assigned to the same assignee as the present invention, disclose various workpiece-surface-influencing device embodiments.
Fixed abrasive sheets or pads, which are supplied by companies such as 3M and which are commonly used in CMP applications, work efficiently on WSID surfaces. Such abrasive sheets are generally comprised of abrasive composites that have a discernible precise shape such as pyramidal or cylindrical. The abrasive composite shapes include a plurality of abrasive grains dispersed in a binder that also bonds abrasive composite shapes to a backing. During a CMP process, as the abrasive sheet is being used to abrade a surface, the abrasive composite shapes break down and expose unused abrasive grains embedded in the binder. As the sheet is used for an extended time period, the composite shapes further break down and expose more abrasive grains. For an ECMPR process, due to the constant breaking down of the abrasive layer, such abrasive sheets have relatively short life time and need to be replaced often. This in turn lowers throughput and also adversely affect product consistency.
Therefore, it will be desirable to provide a longer life abrasive and hard surface for the WSID used in an ECMPR technique.